IEEE 802.16 is a series of Broadband Wireless Access Standards authorized by the IEEE. The IEEE 802.16 family of standards is officially called WirelessMAN, developed for the global deployment of broadband Wireless Metropolitan Area Networks, which is also called WiMAX. IEEE 802.16e is one of the most popular implementation of the IEEE 802.16 standards. The IEEE 802.16e standard addresses “Mobile Broadband Wireless Access System”, also called Mobile WirelessMAN originally defined by the IEEE 802.16e-2005 amendment. The IEEE 802.16e standard essentially standardizes two aspects of the air interface, the physical (PHY) layer and the Media Access Control (MAC) layer. At the PHY layer, IEEE 802.16e uses scalable OFDMA to carrier data, supporting channel bandwidths of between 1.25 MHz and 20 MHz. At the MAC layer, IEEE 802.16e describes a number of connection management functions, mobility management functions and convergence sublayers that defines how data is encapsulated and classified over the air interface.
The IEEE 802.16m standard addresses “Air Interface for Fixed and Mobile Broadband Wireless Access System”. The IEEE 802.16m standard amends the legacy IEEE 802.16e WirelessMAN-OFDMA specification to provide an advanced air interface for operation in licensed bands. It meets the system requirements of IMT-Advanced next generation mobile networks, while provides continuing support for legacy IEEE 802.16e WirelessMAN-OFDMA equipments. The purpose of the IEEE 802.16m standard is to provide performance improvements necessary to support future advanced services and applications, such as the support of 1 Gbps peak transmission rate required by the International Telecommunications Union (ITU-R).
In general, network deployment takes an evolution path, rather than a revolution one. Therefore, it is foreseeable that WiMAX systems will be gradually evolved from legacy IEEE 802.16e systems to IEEE 802.16e and IEEE 802.16m coexisting systems and eventually to 16m-only systems when the IEEE 802.16m standard starts to emerge. During the early stage of the network evolution, 16e-only base stations (BS) have more service coverage than new 16e/16m and 16m-only BSs. While the IEEE 802.16m standard supports legacy IEEE 802.16e-only equipments (i.e., backward compatibility), the IEEE 802.16e standard does not support the capability of future IEEE 802.16m equipments. Therefore, new challenges and problems arise in supporting service continuity between an IEEE 802.16e and IEEE 802.16m coexisting wireless network, which includes features such as scanning and handover.
When a mobile station (MS) handovers from its serving base station (SBS) to a target base station (TBS), the mobile station normally receives neighbor advertisement information (NBR-ADV) broadcasted from the serving base station, scans the neighboring base stations, and selects the target base station from the scanned neighboring cells by either MS or SBS. Unfortunately, a legacy IEEE 802.16e-only base station cannot broadcast any IEEE 802.16m message to inform the mobile station the existence of an IEEE 802.16m-only neighboring cell. Therefore, if the neighboring cells are IEEE 802.16m-only, then the mobile station may be forced to use blind scanning, a more time-consuming and less efficient way, to scan and select its desired IEEE 802.16m target base station. If, however, the neighboring cells have IEEE 802.16e/16m-coexistence capability, then it may become possible for the serving base station to inform the mobile station of the 802.16e/16m-coexistence capability of the neighboring cells.
One possible scheme is to include IEEE 802.16m zone information in IEEE 802.16e neighbor advertisement information, which requires modification of the IEEE 802.16e specification (e.g., MOB_NBR-ADV). Another possible scheme (see C802.16m-08/864r4 and C802.16m-08/646r1 for more detail) is to define a new Downlink Channel Description (DCD) Type Length Value (TLV) message for IEEE 802.16e/16m-coexistence indication, which also requires modification of the IEEE 802.16e specification. In addition, it takes longer delay for the mobile station to discover the coexistence because the DCD TLV message is not broadcasted every frame. Other proposals include carrying IEEE 802.16m zone information using a special IEEE 802.16e message, defining new MAC versions for IEEE 802.16e/16m mixed-mode base station, etc. Each of the proposed methods has its own limitations and thus not desirable.